Electrodeposition of ruthenium

ABSTRACT

A stable, aqueous electrolyte solution, suitable for use in the electrodeposition of ruthenium, characterized in that it comprises an aqueous solution having a pH in the range 1.2 to 3.0 and contains (a) ruthenium ions complexed by an organic acid, (b) sulfamate ions, and (c) ammonium ions.

United States Patent David Roy Mason Ross-on-Wye;

Brian R. Lerwill, Tuffley, both of England 4,07 1

Jan. 19, 1970 Dec. 7, 197 l Engelhard Industries Limited Sutton, Surrey, England inventors Appl. No. Filed Patented Assignee ELECTRODEPOSITION OF RUTIIENIUM 109; 106/1; ll7/130E [56] References Cited UNITED STATES PATENTS 2,057,638 10/1936 Zimmermann et a1 204/47 2,600,175 6/1952 Volterra 204/47 X 3,123,544 3/1964 Blake 204/47 Primary Examiner-G. L. Kapian Attorneys-Samuel Kahn and John G. Kovalich ABSTRACT: A stable, aqueous electrolyte solution, suitable for use in the electrodeposition of ruthenium, characterized in that it comprises an aqueous solution having a pH in the range 1.2 to 3.0 and contains (a) ruthenium ions complexed by an organic acid, b) sulfamate ions, and (c) ammonium ions.

ELECTRODEPOSITION F RUTHENIUM The invention also relates to a method of preparing the electrolyte solution, and with a process for electroplating a metallic article using the electrolyte solution.

Ruthenium, which is a platinum group metal, is a hard metal with high resistance to corrosion. However, ruthenium is difficult to work mechanically. The ruthenium electrolytes which have been made heretofore are difficult to prepare and also tend to give irregular deposits; and moreover the concentration of ruthenium in the electrolyte solution during use thereof must be accurately controlled.

It is an object of the present invention to provide an improved aqueous electrolyte for electrodepositing ruthenium.

Accordingly, the present invention provides a stable, aqueous electrolyte solution, suitable for use in the electrodeposition of ruthenium, which comprises an aqueous solution having a pH in the range 1.2 to 3.0 and containing (a) ruthenium ions complexed by an organic acid, (b) sulfamate ions, and (c) ammonium ions.

The electrolyte solution of the invention can be prepared by a method which comprises heating an aqueous solution containing a ruthenium ([11) compound and an organic acid, and adding sulfamic acid and an ammonium salt to the aqueous solution to form an electrolyte solution having a pH in the range of 1.2 to 3.0.

Ruthenium (lll) compounds which can be used in the method of the invention are, for example, ruthenium (lll) halides, sulfate and nitrate, nitric acid solutions of oxides and hydroxides of ruthenium, organic salts of ruthenium (lll), e.g. ruthenium acetate, and ruthenium (lll) sulfamate. The preferred ruthenium (lll) compound for use in the invention is ruthenium trichloride. The ruthenium (lll) compounds used in the method of the invention can be commercial ruthenium (lll) compounds which may contain various proportions of ruthenium (I1) and ruthenium (IV). The ruthenium (lll) compounds can contain water of crystallization. If necessary, the ruthenium (lll) compounds are given a prior treatment with nitric acid to form a solution before being used in the method of the invention.

Organic acids which can be used in the method of the invention are, for example, mono-, diand tribasic aliphatic carboxylic acids which can contain one or more hydroxyl groups, e.g. acetic acid, citric acid, oxalic acid, tartaric acid, heptonic acid, malic acid, gluconic acid, lactic acid and glycollic acid. The preferred organic acid for use in the method of the invention is acetic acid in which case the amount used is preferably such that the electrolyte contains from 0.1 to 20 grams, more preferably from 0.5 to 5 grams, in total of free and complexed acetic acid per liter of electrolyte solution. The amounts of other organic acids used in the invention are preferably chemically equivalent to the preferred amounts of acetic acid which can be used.

It is preferred to use in the method of the invention an amount of sulfamic acid such that the electrolyte solution contains from to 300 grams, more preferably from to 250 grams, in total of free and complexed sulfamic acid per liter of electrolyte solution.

Also, although the concentration of ruthenium in the electrolyte solution can be varied widely it is preferred that the electrolyte solution should contain from l to 50 grams, more preferably from 5 to grams, of ruthenium per liter of electrolyte solution.

The ammonium salt used in the method of the invention is preferably ammonium sulfamate which is preferably added in an amount such that the electrolyte solution contains from 1 to 75 grams, more preferably from 10 to 30 grams, of ammonium sulfamate per liter of electrolyte solution.

The electrolyte solutions of the invention are preferably prepared from a concentrate which contains 50 or more grams per liter of ruthenium, the concentrate being used to replenish the electrolyte solution during use thereof. A concentrate can be prepared as follows: an aqueous solution containing 500 grams of ruthenium, as ruthenium trichloride, is treated with from 30 to 50 ml. of acetic acid. The resulting solution is refluxed for 2 hours, after which 1,940 grams of sulfamic acid are added, and the solution thus formed heated for a further three hours. 250 grams of ammonium sulfamate are then added and the resulting solution is concentrated to give a concentrate containing 50 or more grams per liter of ruthenium.

To produce an electrolyte solution according to the invention the concentrate is diluted to a ruthenium concentration in the range 1 to 50 grams, preferably from 5 to 20 grams, per liter of electrolyte solution. During dilution, approximately 1 gram of ammonium sulfamate is added for each gram of ruthenium present in the concentrate.

The pH of the electrolyte solution is adjusted to a value in the range 1.2 to 3.0, preferably between 1.6 and 2.0, by the addition of dilute ammonia solution (5-10 percent ammonia) to obtain an electrolyte solution in accordance with the invention. The preparation of electrolyte solutions in accordance with the invention from the concentrate prepared as described above, and the use of the thus obtained electrolyte solutions is illustrated by the examples set forth hereinafter.

The invention also provides a process for electroplating the surface of a metallic article with ruthenium, using an electrolyte solution of the present invention. The cathode in the electroplating process is the article the surface of which is to be plated, and the anode can be, for example, a platinum or platinized titanium anode. If desired, the surface of the metallic article can be coated with gold before the article is electroplated in the ruthenium electrolyte solution. The electrolyte solution can be used at temperatures from 20 to C., and is preferably used at temperatures from 60 to 70 C. The pH of the electrolyte solution is controlled so as to lie in the range of 1.2 to 3.0, preferably between 1.6 and 2.0, during electrodeposition. Cathode current densities of from 0.54 to 5.4 a./sq.dm. can be used, although it is preferred to use cathode current densities of from 1.1 to 2.2 a./sq.dm. The cathode efficiencies using the electroplating process of the invention range from 40 to 75 percent.

It is possible by use of an electrolyte solution of the invention to obtain ruthenium deposits having a hardness of between 800 and 900 HV (Hardness Vickers) and a thickness of up to 5 microns without severe cracking.

The following examples illustrate the invention.

EXAMPLE 1 milliliters of the concentrate prepared as described above and 5 grams of ammonium sulfamate were added to water. The pH of the solution was adjusted to 2.0 with 50 percent ammonium hydroxide solution, and the solution was then diluted with water to a volume of 1 liter to give a solution having a pH of 2.0. This solution was used as the electrolyte in the electrodeposition of ruthenium under the following conditions:

Temperature 70 C. Cathode Current Density 2.2 ampslsqdm. Anode Platinum Cathode Polished brass plated with l-2 u of gold Time 20 minutes.

At the end of the electroplating, a bright adherent coating of ruthenium having a thickness of 0.00017 inch (4.23 p.) had been deposited onto the cathode. Calculation showed that the cathode efficiency was 41 percent.

EXAMPLE 2 200 milliliters of the concentrate prepared as described above and 10 grams of ammonium sulfamate were added to water. The pH of solution was adjusted to 2.0 with 50 percent ammonium hydroxide solution, and the solution was diluted with water to a volume of 1 liter to give a solution having a pH of 2.0. This solution was used as the electrolyte in the electrodeposition of ruthenium under the following conditions:

Temperature 70 C. Cathode Current Density l.l amps/sqdm. Anode Platinum Cathode Polished brass plated with l-2 p, of

gold Time l minutes At the end of the electroplating, a bright adherent coating of ruthenium having a thickness of 0.00006 inch (1.52 ,1.) had been deposited into the cathode. Calculation showed that the cathode efficiency was 58.4 percent.

EXAMPLE 3 240 milliliters of the concentrate prepared as described above and 12 grams of ammonium sulfamate were added to water. The pH of the solution was adjusted to 2.0 with 50 percent ammonium hydroxide solution, and the solution was diluted with water to a volume of 1 liter to give a solution having a pH of 2.0. This solution was used as the electrolyte in the electrodeposition of ruthenium under the following conditions:

Temperature 70 C. Cathode Current Density l.l ampslsq.dm. Anode Platinum Cathode Polished brass plated with 2 of gold Time minutes At the end of the electroplating, a bright adherent coating of ruthenium having a thickness of 0.000075 inch (1.90 1.1.) had been deposited into the cathode. Calculation showed that the cathode efiiciency was 73.0 percent.

EXAMPLE 4 400 milliliters of the concentrate prepared as described above and grams of ammonium sulfamate were added to water. The pH of the solution was adjusted to 2.0 with 50 percent ammonium hydroxide solution and the solution was diluted with water to a volume of 1 liter to give a solution having a pH of 2.0. This solution was used as the electrolyte in the electrodeposition of ruthenium under the following conditions:

Temperature 70 C. Cathode Current Density l.l amps/sq.dm. Anode Platinum Cathode Polished brass plated with l2 p, of

gold Time 10 minutes.

At the end of the electroplating, a bright adherent coating of ruthenium having a thickness of 0.000045 inch (1.14 .4.) had been deposited onto the cathode. Calculation showed that the cathode efiiciency was 43 percent.

It will be seen from the above examples that despite wide variations in the operating conditions, no anode staining or precipitation took place and ruthenium deposits were obtained which were bright, firmly adhered to the substrate and free from irregularity.

What we claim is:

l. A stable, aqueous electrolyte solution, suitable for use in the electrode position of ruthenium, which comprises an aqueous solution having a pH in the range 1.2 to 3.0 and containing (a) l to 50 grams per liter of ruthenium complexed by 0.1 to 20 grams per liter carboxylic acid, (b) 10 to 300 grams per liter sulfamic acid, (c) l to 75 grams per liter of ammonium sulfamate and d) sufficient ammonium hydroxide to provide said pH.

2. An electrolyte solution as claimed in claim 1, in which the carboxylic acid is a mono-, dior tribasic aliphatic carboxylic acid.

3. An electrolyte solution as claimed in claim 2, in which the carboxylic acid is acetic acid.

4. An electrolyte solution as claimed in claim 3, which contains from 0.5 to 5 grams in total of free and complexed acetic acid per liter of electrolyte solution.

5. An electrolyte solution as claimed in claim 2, in which the carboxylic acid contains one or more hydroxyl groups.

6. An electrolyte solution as claimed in claim 1, which contains from 5 to 20 grams of ruthenium per liter of electrolyte solution.

7. An electrolyte solution as claimed in claim 1, which contains from 15 to 250 grams in total of free and complexed sulfamic acid per liter of electrolyte solution.

8. An electrolyte solution as claimed in claim 1, which contains from 10 to 30 grams of ammonium sulfamate per liter of electrolyte solution.

9. A method of preparing a stable, aqueous electrolyte solution suitable for use in the electrodeposition of ruthenium, which comprises heating an aqueous solution containing a ruthenium Ill compound in which the amount of ruthenium 11! compound used is such that the electrolyte solution contains from 1 to 50 grams per liter of ruthenium and 0.1 to 20 grams per liter carboxylic acid, and adding 10 to 300 grams per liter of sulfamic acid and l to 75 grams per liter of ammonium sulfamate to the aqueous solution and sufficient ammonium hydroxide to form an electrolyte solution having a pH in the range of 1.2 to 3.0.

10. A method according to claim 9, in which the carboxylic acid is a mono-, di-or tribasic aliphatic carboxylic acid.

11. A method according to claim 10, in which the carboxylic acid is acetic acid.

12. A method according to claim 11, in which the amounts of acetic acid used is such that the electrolyte solution contains from 0.5 to 5 grams in total of free and complexed acetic acid per liter of electrolyte solution.

13. A method according to claim '10, in which the carboxylic acid contains one or more hydroxyl groups.

14. A method according to claim 9, in which the ruthenium (lll) compound is ruthenium trichloride.

15. A method according to claim 9, in which the amount of ruthenium (lll) compound used is such that the electrolyte solution contains from 5 to 20 grams of ruthenium per liter of electrolyte solution.

16. A method according to claim 9, in which the amount of sulfamic acid used is such that the electrolyte solution contains from 15 to 250 grams in total of free and complexed sulfamic acid per liter of electrolyte solution.

17. A method according to claim 9, in which the amount of ammonium sulfamate used is such that the electrolyte solution contains from 10 to 30 grams of ammonium sulfamate per liter of electrolyte solution.

18. A process for electroplating a surface of a metallic article with ruthenium, which comprises electrodepositing ruthenium onto the surface of the metallic article from an electrolyte solution as claimed in claim l.

19. A process according to claim 18, in which the cathode current density used is from 0.54 to 5.4 a./sq.dm.

20. A process according to claim 18, in which the temperature of the electrolyte solution is from 60 to 70 C.

l IF t 

2. An electrolyte solution as claimed in claim 1, in which the carboxylic acid is a mono-, di- or tribasic aliphatic carboxylic acid.
 3. An electrolyte solution as claimed in claim 2, in which the carboxylic acid is acetic acid.
 4. An electrolyte solution as claimed in claim 3, which contains from 0.5 to 5 grams in total of free and complexed acetic acid per liter of electrolyte solution.
 5. An electrolyte solution as claimed in claim 2, in which the carboxylic acid contains one or more hydroxyl groups.
 6. An electrolyte solution as claimed in claim 1, which contains from 5 to 20 grams of ruthenium per liter of electrolyte solution.
 7. An electrolyte solution as claimed in claim 1, which contains from 15 to 250 grams in total of free and complexed sulfamic acid per liter of electrolyte solution.
 8. An electrolyte solution as claimed in claim 1, which contains from 10 to 30 grams of ammonium sulfamate per liter of electrolyte solution.
 9. A method of preparing a stable, aqueous electrolyte solution suitable for use in the electrodeposition of ruthenium, which comprises heating an aqueous solution containing a ruthenium III compound in which the amount of ruthenium III compound used is such that the electrolyte solution contains from 1 to 50 grams per liter of ruthenium and 0.1 to 20 grams per liter carboxylic acid, and adding 10 to 300 grams per liter of sulfamic acid and 1 to 75 grams per liter of ammonium sulfamate to the aqueous solution and sufficient ammonium hydroxide to form an electrolyte solution having a pH in the range of 1.2 to 3.0.
 10. A method according to claim 9, in which the carboxylic acid is a mono-, di- or tribasic aliphatic carboxylic acid.
 11. A method according to claim 10, in which the carboxylic acid is acetic acid.
 12. A method according to claim 11, in which the amounts of acetic acid used is such that the electrolyte solution contains from 0.5 to 5 grams in total of free and complexed acetic acid per liter of electrolyte solution.
 13. A method according to claim 10, in which the carboxylic acid contains one or more hydroxyl groups.
 14. A method according to claim 9, in which the ruthenium (III) compound is ruthenium trichloride.
 15. A method according to claim 9, in which the amount of ruthenium (III) compound used is such that the electrolyte solution contains from 5 to 20 grams of ruthenium per liter of electrolyte solution.
 16. A method according to claim 9, in which the amount of sulfamic acid used is such that the electrolyte solution contains from 15 to 250 grams in total of free and complexed sulfamic acid per liter of electrolyte solution.
 17. A method according to claim 9, in which the amount of ammonium sulfamate used is such that the electrolyte solution contains from 10 to 30 grams of ammonium sulfamate per liter of electrolyte solution.
 18. A process for electroplating a surface of a metallic article with ruthenium, which comprises electrodepositing ruthenium onto the surface of the metallic article from an electrolyte solution as claimed in claim
 1. 19. A process according to claim 18, in which the cathode current density used is from 0.54 to 5.4 a./sq.dm.
 20. A process according to claim 18, in which the temperature of the electrolyte solution is from 60* to 70* C. 